I planted 2 blackberry bushes that vine out this past spring and they grew great but, of course, no berries yet. I have only seen how to prune them after they have had berries. How do I cut them back this first year?
Pruning Blackberry Bushes
Certified GKH Gardening Expert
I would leave the Blackberries for now and prune them in the early spring.
Make sure you identify the type of berries that you have planted.
Here are links for you.